Abstract: The composite ground formed by the cement-fly ash-gravel (CFG) columns has the advantage of fast construction, short installation period, easy to control the quality and lost construction. This method has widely used as the foundation that supporting the high-raised residential buildings in Beijing. The Changxindian area is located in the west rolling area of Beijing. The shallow deposited bedrock consists of highly weathered to moderately weathered breccia, and soft rock such as mudstone. This paper presents a case history of design of CFG columns as the composited ground in Changxindian area in the shallow bedrock geological formations. The design applied varying CFG column lengths by socked the CFG columns of 0.5 to 1.0 meters into the strongly weathered bedrock. The paper also presents the preliminary design analyses and the ground improvement related column diameters, column length, center-to-center spacing, replacement ratio, column material composition and cushion zone thickness.

Key words: changxindian area, CFG columns, composited ground, varying column lengths